Whole house audio problem - Easy fix??? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 11 Old 07-10-06, 09:31 PM
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Question Whole house audio problem - Easy fix???

I've decided to add a second pair of speakers to our deck. The existing speakers are connected the a Knoll volume control which gets its feed from a 12 zone speaker selector. Instead of running a second volume control (off the speaker selector) for the new deck speakers, I'd like to use the one existing volume control for both.

Since I have an extra amp available, I though the easy way to do this would be to take the line from the existing volume control and send its output to the speaker level input on a seperate amp (AudioSource Amp200). This amp would then send sound to the first set of speakers through the A channel and the new set would be powered by the B channel.

When I did a test run this way. I found that the volume control had lost its range of control. It seems like the first click on the volume control is 70% of full volume.

I've drawn a diagram of how the wiring is set up.

What am I doing wrong that would cause the volume control to lose its range?

Thanks
Joe

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post #2 of 11 Old 07-10-06, 11:35 PM
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Re: Whole house audio problem - Easy fix???

Hey Joe... I'm not sure what might be going on but wanted to welcome you to the Shack. Surely one of our technical gurus can help ya figure it out.

My thinking is that you are increasing the speaker level input to the amp which is much more (or maybe it's less) sensitive than controlling the volume of the speakers themselves.

I would say remove the VC to the amp and connect the speakers leads and then use the amp volume control... if none then use the VC's after the amp.

But I'm a hillbilly and
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post #3 of 11 Old 07-11-06, 08:37 AM
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Re: Whole house audio problem - Easy fix???

Joe,

The 'speaker level' or 'high level' input on any amplifier does not reflect the impedance properties of a speaker coil. Your volume control (sourced from your main amplifier) is expecting to see a speaker load. A speaker presents a frequency dependant resistance (impedance) nominally about 8 ohms. The signal from a power amplifier is a relatively high voltage and can supply rather large amounts of current. This power is normally dissipated in the speaker load.

To accommodate the fact that there are situations when a user has no line level signal available to feed a power amplifier, some manufacturers provide a convenient 'high level' input interface. It is usually nothing more than a cheap voltage divider to reduce the voltage to a more manageable line level that the amplifier can deal with. Because this interface presents a high impedance to the amplifiers output that is sourcing the signal, there is little to no current drawn and hence low power levels are dissipated in this interface.

The input speaker level voltage divider design has an expectation of certain voltage swings, but can't anticipate what your amplifier and volume control will feed it, so even a small amount of voltage from your system may produce a large volume to the patio amplifier. Your main amplifier and volume pad also have a certain anticipation of being provided an 8 ohm load to operate properly. The fact that you're not providing this load (rather a high impedance speaker level interface load), then the designed voltage output will also be affected.

You can prove this by placing a speaker directly across the output of the volume control in parallel with the amplifiers speaker level input. Now you've provided a proper impedance match. You'll see that the patio amplifier now operates as you wanted. But of course you have the sound from that parallel speaker to deal with. Yes, you could use a resistive load, but then you have its power dissipation to deal with, so I wouldn't go there - could be dangerous heat levels.

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post #4 of 11 Old 07-11-06, 08:54 AM
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Re: Whole house audio problem - Easy fix???

Thanks for the advice. Is there any work-around for this situation that would allow me to control both sets of speakers from a single volume control?

Would a line-level convertor resolve this issue?

I have one on my home theater that is used to provide a signal to an amp that powers a pair of Clark transducers. The transducer "volume" always coincides with the front mains (from where the line level convertor is attached).

Your help is greatly appreciated.

Joe
post #5 of 11 Old 07-11-06, 09:27 AM
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Re: Whole house audio problem - Easy fix???

Quote:
Would a line-level convertor resolve this issue?
Not likely, that's basically what is being used on the speaker level input to your amplifier.

Quote:
Is there any work-around for this situation that would allow me to control both sets of speakers from a single volume control?
For sure. You can simply hook two speakers to the output of the volume control as long as you don't exceed the specifications of the main amplifier. This calculation would depend on the nominal impedance of the two speakers in question and the minimum speaker impedance allowed for your amplifier. These two values would determine whether you connected the two speakers in parallel or series. Either way will work.

As long as the resulting impedance of the two speakers in parallel didn't exceed the minimum impedance allowed by your amplifier, then this would provide the best sound quality. Connecting the two in series would be easier on the amplifier, but not provide as good a response, although I don't know that speakers on a deck are really considered critical listening.

What is the minimum allowed impedance for your amplifier? and what is the nominal impedance of the two speakers in question? I assume you understand the difference between connecting two speakers in series or parallel?

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post #6 of 11 Old 07-11-06, 09:29 AM
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Re: Whole house audio problem - Easy fix???

Hi Joe,

brucek is right on in his analysis. I might add the following with regard to your specific problem.

Your CD player is feeding its line level signal to AMP1, and AMP1 is then running wide open to each of your speakers, using in-line VCs to set each set of speaker's levels. Nothing wrong there necessarily.

I think the problem is the signal that you're feeding to AMP2, from AMP1. As brucek said, AMP2 is trying to deal with a large range of input signals, and can't necessarily anticipate what might be coming at it. I would imagine that it wouldn't normally be presented with a full volume speaker-level signal. Even though you are attenuating with the VC, I'm not sure what that's doing to the input signal to AMP2.

So -- can you attenuate the signal at AMP1? Does it have a gain control? That would make the speakers attached to AMP1 generally "quieter", but what's the max you've ever hit on the VCs between AMP1 and its speakers?

Can you attenuate the signal coming from the CD player? Some have variable outputs, but it's not very common.

Here's another thought, and I really don't know what will happen -- what if you used two VCs in a cascade between AMP1 and AMP2? Never tried anything like it, but it might give you "coarse" and "fine" levels of control over AMP2.

You may also consider changing some equipment around. For my "other room", I'm using some in-ceiling speakers for background music. I don't necessarily expect a high-end sound in those rooms; I have my main room for that. If you're in the same boat, pick up a used receiver or preamp (eBay, craigslist, etc.) and use that to set volume levels for wherever you need it.

As Sonnie suggested, try placing the VC between AMP2 and its speakers. That would probably be pretty easy, although I would really have some concern over running AMP2 with such a hot input signal all the time.

OK, OK, I'm almost done here -- why use AMP2 at all? Are you limited by the speaker selector, AMP1 or wiring in the house? Why not go straight from the final VC (that's feeding AMP2) right into the speakers that AMP2 would power?



Good luck!

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post #7 of 11 Old 07-11-06, 10:03 AM
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Re: Whole house audio problem - Easy fix???

Thanks for the info guys.

Here's some more info for Brucek...
The main speakers are 8 ohms, the new speakers are 4 ohms, and the amp says this...
80 watts at 8 ohms, 125 watts at 4 ohms, and "stable at 2 ohms". (whatever that means)

I'm vaguely familiar with wiring in series or parrallel. I'd have to pull out an old text book I guess.

Otto, amp 1 does have gain control on the back. I have it 1/3 up. I wont be able to attenuate the CD source though.

I do know that I can use two volume controls inline with each other. We currently have the hall way speakers being controlled this way from upstairs and downstairs (so it can be turned down easily if the phone rings).

The speaker selector still has room for more zones but I really dont want to install another volume control for the new deck speakers.


Now I'm thinking of trying the line level convertor but in a more traditional sense...

How about running the deck main speakers off the selector (the way it was when it worked fine). Then attaching a line level convertor off the signal going to the speakers from the VC. Then running the line level feed into the amp2 which would then only power the new speakers. Since the amp2 would have gain and volume control, I figure I could make the gross adjustment on the amp. The line level convertor should be able to do the rest to keep the new speakers matched in volume to the old ones.

What do you think?



Joe
post #8 of 11 Old 07-11-06, 10:28 AM
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Re: Whole house audio problem - Easy fix???

Quote:
What do you think?
No.

Quote:
the new speakers are 4 ohms, and the amp says this
Perfect. Wire it like this and it will be fine.




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post #9 of 11 Old 07-11-06, 10:49 AM
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Re: Whole house audio problem - Easy fix???

Thanks for the image. I appreciate it.
Now I'm confused. How does that image related to using 2 pairs of speakers?

Also, any reason why my idea with the LLC wouldnt work?
I know it sounds like I'm hell-bent on using the LLC. Sorry.
post #10 of 11 Old 07-11-06, 11:54 AM
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Re: Whole house audio problem - Easy fix???

Quote:
Now I'm confused. How does that image related to using 2 pairs of speakers?
Well, I've only shown one channel. I assumed you were using a stereo amplifier and a stereo volume control and were using a left and right speaker. Now you want to add another set of speakers to that same setup.

As such, in the interest of clarity, I've drawn one channel only - for example the Left channel. The right channel will be wired the same.

Am I confused about the situation?

Quote:
Also, any reason why my idea with the LLC wouldnt work?
It's just completely not neccessary. You're adding amplifiers and convertors that aren't needed for the solution.

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